The present invention relates, according to an aspect thereof, to vehicles having multiple drive axles and, more particularly, to such vehicles having one or more raisable and lowerable rear drive axles.
Multiple drive axle trucks and tractors are often referred to as 6×4, 6×6, 8×6, 8×8, 10×8, and 10×10 configurations. A 6×4 configuration, for example, has three axles, with two of the axles being driven axles. Most current commercial trucks and tractors having multiple drive axles are designed to carry substantial loads. While they may carry heavy loads at or close to their maximum loading from point A to point B, they often carry substantially less than their maximum load after unloading at point B.
Trucks and tractors are often designed with, for example, 6×4 configurations instead of 4×2 configurations due to restrictions on axle drivehead load carrying capacities, as well as better maneuverability of 6×4's in adverse weather conditions. A 6×4 configuration will permit input torque from the transmission of the vehicle to be split between the two axle driveheads, thus tending to decrease wear and tear on the drivehead's gears when the truck/tractor carries heavier loads. However, when carrying lighter loads that could be handled by a 4×2 configuration, each of the axle driveheads sees less transmission input torque than what they are designed to handle. Nonetheless, each of the driveheads requires energy to drive the drivehead, the driveheads are both subject to wear and tear due to use, and damage such as false Brinell damage or fretting can occur to structures such as universal joint bearings due to prop-shaft vibration and light loads.
It is desirable to provide a multiple drive axle vehicle that can be converted from one configuration, such as a 6×4, to another configuration, such as a 4×2, depending upon load on the vehicle or the engine.
According to an aspect of the present invention, a vehicle having a multiple drive axle assembly comprises a forward axle assembly comprising a forward interaxle differential, a forward interaxle differential input shaft, a first forward interaxle differential output shaft, and a second forward interaxle differential output shaft, the forward interaxle differential distributing power from the forward interaxle differential input shaft between the first and the second forward interaxle differential output shafts, an intermediate drive shaft connected to the second forward interaxle differential output shaft, a rear axle assembly comprising a rear differential and a rear differential input shaft, and a rear clutch arrangement between the intermediate drive shaft and the rear differential input shaft, the rear clutch arrangement being movable between a first position in which the rear clutch arrangement rotationally locks the intermediate drive shaft and the rear differential input shaft and a second position in which the intermediate drive shaft and the rear differential input shaft are rotationally disconnected.
According to another aspect of the present invention, a vehicle having a multiple drive axle assembly comprises a forward axle assembly comprising a forward interaxle differential, a forward interaxle differential input shaft and a forward interaxle differential output shaft, an intermediate drive shaft connected to the forward interaxle differential output shaft, a rear axle assembly comprising a rear differential and a rear differential input shaft, and a rear clutch arrangement between the intermediate drive shaft and the rear differential input shaft, the rear clutch arrangement being movable between a first position in which the rear clutch arrangement rotationally locks the intermediate drive shaft and the rear differential input shaft and a second position in which the intermediate drive shaft and the rear differential input shaft are rotationally disconnected.
According to yet another aspect of the present invention, a method of operating a vehicle having a multiple drive axle assembly comprises dividing power from a forward interaxle differential input shaft between a first forward interaxle differential output shaft associated with a forward axle assembly and a second forward interaxle differential output shaft associated with a rear axle assembly via a forward interaxle differential, transmitting power to a rear differential input shaft of a rear differential of the rear axle assembly via an intermediate drive shaft connected to the second forward interaxle differential output shaft, and rotationally disconnecting the intermediate drive shaft and the rear differential input shaft.